1. Field of the Invention
The present invention relates to a dry-type toner for developing latent electrostatic images in the field of electrophotography, electrostatic recording and electrostatic printing, and particularly to a dry-type toner for developing latent electrostatic images, comprising as a negative charge controlling agent a metallic salt compound.
2. Discussion of Background
For developing latent electrostatic images formed on an electrophotographic photoconductor or electrostatic recording member to visible toner images, there are conventionally proposed two methods: a wet-type developing method using a liquid type developer, and a dry-type developing method using a dry-type developer. This dry-type developer includes one-component dry-type developer comprising a toner obtained by dispersing a coloring agent such as a dye and a pigment in a binder resin; and a two-component dry-type developer obtained by mixing the above-mentioned toner and carrier particles. These methods have individually their own advantages and shortcomings. Recently, the dry-type developing method is more prevalant than the wet-type developing method.
When the above-mentioned dry-type developer is prepared by merely dispersing a coloring agent in a binder resin, the desired chargeability cannot be obtained. Therefore, a proper amount of a charge controlling agent is generally added to the dry-type developer.
Examples of the conventional charge controlling agent are as follows:
(1) Charge controlling agents which apply a positive charge to the toner; PA0 (2) Charge controlling agents which apply a negative charge to the toner;
Oil-soluble nigrosine dye, quaternary ammonium salt, azine-type dye having an alkyl group, basic dye, and basic dye lake. PA1 Metal-containing dye, for example, chromium-containing monoazo complex, chromium-containing salicylic acid compound complex, and chromium-containing organic dye such as copper phthalocyanine green and chromium-containing monoazo dye.
These conventional charge controlling agents exhibit satisfactory charge controlling performance at the initial stage when the toners comprising such charge controlling agents are used in the electrophotographic process. However, the charge controlling performance of the conventional charge controlling agents is deteriorated and triboelectric chargeability of the toner is decreased in the course of repeated use thereof, with the result that the quality of obtained toner images gradually becomes poor.
In addition, such conventional charge controlling agents are separated from the toner particles due to the friction between toner particles and between the toner particle and the surface of a photoconductor, and the collision of the toner particles with carrier particles. The charge controlling agents which have been separated from the toner are deposited on the surface of the photoconductor, and as a result, the so-called toner-filming phenomenon takes place. Particularly, the toner-filming phenomenon is apt to occur at high temperatures and high humidities.
As previously mentioned, most of the conventional charge controlling agents are coloring materials, so that each charge controlling agent can only be used for a toner whose color is the same as that of the charge controlling agent. When a color toner is prepared by containing the conventional charge controlling agents therein, clear color images cannot be readily obtained.